Methodology for evaluating the transition process dynamics towards 4th generation district heating networks Anna Volkova * , Vladislav Ma  satin, Andres Siirde Tallinn University of Technology, Department of Energy Technology, Ehitajate tee 5,19086, Tallinn, Estonia article info Article history: Available online 23 February 2018 Keywords: Consumers District heating networks Smart thermal grids Low temperature Smart energy Key performance indicators 4GDH abstract Currently, the 4th Generation District Heating (4GDH) is an attractive topic in the energy field as it concerns a sustainable and efficient means of delivering heat to houses. The 4GDH concept is charac- terised by low temperatures, low heat distribution losses, renewable and excess energy utilisation, as well as high efficiency. As a result of implementing the 4GDH concept, existing district heating systems (DHS) are undergoing massive improvement. The barriers faced by existing DHS over the course of the transition process towards the 4th generation are reviewed in the paper; the methodology for the evaluation of the DHS transition process towards the 4th generation is also presented. This methodology allows to assess the transition process dynamics, as well as helps to focus on DHS characteristics, which need to be improved. A large-scale DHS in Tallinn (Estonia) was analysed with the help of the proposed methodology. Supply and return temperatures, the share of renewable energy, and network conditions demonstrated the highest potential for improvement and had the most notable impact on the Tallinn DHS transition process. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction District heating (DH) has been widely used for space heating and in domestic hot water supply for many decades [1]. Nowadays, there appear to be promising possibilities for DH in future energy sector developments; however, DH must be renewed and subjected to major improvements [2]. After summarising the ideas concerning the required improve- ments for the future sustainable development of DH, a group of researchers proposed the concept of the 4th Generation District Heating (4GDH) in 2014 [3]. According to this concept, future dis- trict heating systems (DHS) must be able to:  supply low temperature for space heating and domestic hot water supply to buildings (i.e., low-temperature space heating and low-temperature hot water heating, intelligent control in buildings, etc.);  distribute heat over networks with low heat losses (low-tem- perature network, smaller pipe dimensions, improved insu- lation, intelligent control and metering);  enlarge the share of renewable (non-fuel) energy heat sources (solar and geothermal heat) and recycle heat from low- temperature sources (heat from combined heat and power production (CHP) and waste incineration, excess heat, geothermal heat, central solar heat with seasonal thermal en- ergy storage (TES));  become an integrated part of smart energy systems, including smart electricity, gas, thermal grids and district cooling (CHP coupled with TES, large-scale heat pumps in CHP, with inte- grated CHP plants involved in securing grid stabilisation tasks);  ensure proper planning, cost and motivation structures (inte- grated strategic infrastructure planning, GIS system-based planning, tariffs based on long-term costs). Despite the fact that the 4GDH concept has already been implemented in European DHS, there are still numerous DHS that can be described as 2nd or 3rd generation networks. The main questions that should be answered are: Why is the transition process so slow? What are the obstacles, as well as possible solu- tions in transitioning to the 4GDH, and how can the DHS transition process be evaluated? In recent years, existing DHSs have been * Corresponding author. Tallinn University of Technology, School of Engineering, Department of Energy Technology, Building U06, Room 227, Ehitajate tee 5,19086, Tallinn, Estonia. E-mail address: anna.volkova@ttu.ee (A. Volkova). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy https://doi.org/10.1016/j.energy.2018.02.123 0360-5442/© 2018 Elsevier Ltd. All rights reserved. Energy 150 (2018) 253e261